Such a device is known, for example, from DE 10 2007 045 512 A1, which is incorporated by reference. In said document, a pole of a car battery is connected to the body by a cable. A shunt is located between the cable and the pole of the car battery. As is described, for example, in DE 10 2004 033 836 B3, which is incorporated by reference, the voltage drop across this shunt is supplied to a measuring apparatus in order to thus determine the current which is flowing through the shunt. The advantage of the shunt consists in that its resistance is largely temperature-independent. However, this results in costs which are not inconsiderable.